1. Field of the Invention
The present general inventive concept generally relates to a fixing unit and an image forming apparatus including the fixing unit, and more particularly, to a fixing unit including a heating roller and a pressurizing roller, and an image forming apparatus including the fixing unit.
2. Description of the Related Art
An image forming apparatus, such as a printer, a fax machine, a copier, a multifunction peripheral (MFP), or the like, forms an image on a printing medium using an electrophotographic method. The image forming apparatus forms the image on the printing medium through charging, exposing, developing, transferring, and fixing processes.
In the fixing process, the image on the printing medium is fixed on the printing medium by a fixing unit. In general, the fixing unit includes a heating roller and a pressurizing roller to apply heat and pressure, which are necessary for fixing the image, to the printing medium. The heating roller and the pressurizing roller are disposed to face each other. Also, when the printing medium passes between the heating roller and the pressurizing roller, heat and pressure are applied to the printing medium to fix the image on the printing medium.
The pressurizing roller may have a hollow pipe shape in which a heating source, such as a heating resistor or a heating lamp, is disposed. The pressurizing roller is formed of a metal material, such as aluminum (Al) or steel, having high heat conductivity.
A time required for heating the heating roller from a room temperature to a fixing temperature is referred to as a warm-up time (WUT). A time required for performing printing on a first printing medium, i.e., a first page print out time (FPOT), increases with an increase in the WUT.
The heating roller has a hollow pipe shape, and a thickness of the heating roller may be reduced to reduce heat capacity of the heating roller in order to reduce a WUT. For example, the thickness of the heating roller may be reduced to be equal to or less than about 0.8 mm.
However, if the thickness of the heating roller is reduced to be equal to or less than 0.8 mm, the heating roller does not endure a pressurizing force of the pressurizing roller facing the heating roller and thus may cause deformation or fatigue failure thereof. In this case, durability and lifespan of the heating roller are reduced.